The present invention relates to two cycle internal combustion engines and more particularly to crankcase-pumped engines.
Many design modifications have been made in crankcase-pumped two cycle internal combustion engines in order to increase their efficiency and to thus increase the power output from the engines. One of the most severe difficulties with engines of this type is the normal requirement that intake and exhaust gases both flow through ports at the lower end of the cylinder which are opened and closed by action of the piston.
These prior art engines operate with reduced engine efficiency, since it is extremely difficult to totally scavenge exhaust gases from the cylinder without wasting excessive amounts of intake fuel when the intake and exhaust ports are opposite one another at one end of the cylinder wall. Furthermore, free flow of intake and exhaust gases through multiple ports is often not possible with such engines, since, in order to scavenge exhaust gases, it is often necessary that the exhaust and intake ports be diametrically opposed in the cylinder wall.
While it has been common in the prior art to place a valve in the intake port of the crankcase in order to intermittently permit flow of a fuel mixture from a carburetor or other fuel mixing device to the crankcase, the piston itself customarily valves the channel between the crankcase and the cylinder, as well as exhaust ports. The convenience and simplicity of this valving arrangement has apparently discouraged attempts to increase the exhaust gas scavenging efficiency by relocating the intake or exhaust ports in the cylinder. The rare attempts in the prior art to properly valve the channel between the crankcase and the intake port, without using the piston as a valving member, have operated inefficiently because of the slow speed valving arrangements utilized. In addition, these prior art valving systems are unsatisfactory for limiting the compression volume and assuring that explosions will not occur in the crankcase. In regard to the latter problem, it will be recognized that the connection of an intake manifold between the pumping crankcase and an intake port may subject the crankcase to hot combustion gases, which may lead to dangerous explosions within the crankcase.